#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
  
void error_handling(char *message);
  
int main(int argc, char *argv[])
{
    int serv_sock;
    int clnt_sock;
  
    struct sockaddr_in serv_addr;
    struct sockaddr_in clnt_addr;
    socklen_t clnt_addr_size;
  
    char message[] = "Hello world!";
  
    if (argc != 2)
    {
        printf("Usage: %s <port>\n", argv[0]);
        exit(1);
    }
  
    serv_sock = socket(AF_INET, SOCK_STREAM, 0);
    if (serv_sock == -1)
        error_handling("sock() error");
  
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(atoi(argv[1]));
  
    if (bind(serv_sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) == -1)
        error_handling("bind() error");
  
    if (listen(serv_sock, 5) == -1)
        error_handling("listen() error");
  
    clnt_addr_size = sizeof(clnt_addr);
    clnt_sock = accept(serv_sock, (struct sockaddr *)&clnt_addr, &clnt_addr_size);
    if (clnt_sock == -1)
        error_handling("accept() error");
  
    write(clnt_sock, message, sizeof(message));
    close(clnt_sock);
    close(serv_sock);
  
    return 0;
}
  
void error_handling(char *message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}
